DESCRIPTION Dr. Poon and co-workers seek to determine whether heart rate variability is due to the presence of deterministic chaos or if it is due only to sheer randomness. The investigators will follow a three step plan: (1) to obtain a general reliable analytical technique for detecting chaos in the presence of random noise; (2) to apply this and other advanced techniques to the analysis of heart rate data derived from animals; and (3) to apply these techniques to heart rate and arrhythmia data derived from patients. Chaos detection will be performed using (1) a Volterra series expansion with colored (correlated) noise in the embedding space, (2) identifying system parameters using maximum likelihood, and (3) selecting the most probable models according to some information measures.